Probing hydrogen bond netowrk formation in anion-water clusters through high energy collision experiments

摘要

In high-energy collisions (50 keV in the laboratory system) between anion-water clusters [X~-(centre dot)(H_2O)_n, X~- = Cl~-, CN~-, O_2~-,NO_2~-,NO_3~-; n=1-6] and argon, H_3O~+ is formed with an abundance that is determined by the cluster size-the larger the cluster, the more H_3O~+. The mechanism for H_3O~+ formation is believed to be a nearly vertical ionization process (two-electron stripping) followed by an exothermic intracluster hydrogen transfer reaction between an ionized water and a neutral water. The abundance of H_3O~+ can be used as a probe to determine how extended the water hydrogen bond network is in the initial anion-water cluster and to distinguish between surface solvation (water network preserved) and internal solvation (water network broken). In this work, it is demonstrated that in the hydration of hexacyanoplatinate(IV) dianion complexes, surface solvation is important despite the large number of available water binding sites; however, the competition between a cyanide-bound wate rand a "naked" cyanide ligand for a water molecule favors the cyanide-bound water because of the splitting of the excess charges between six ligands (between - 1/3 and -1 charge at each ligand on average). We also investigate anion-methanol clusters in which the hydrogen bond network is less extended with the result of a less abundant oxonium ion compared to the hydronium ion from similar size water clusters.